Magnetorheologic Clutch

ABSTRACT

A magnetorheological clutch comprises a stationary part ( 1 ), of a rotatable primary part ( 2 ) with primary lamellae ( 3 ) and of a secondary part ( 8 ) with secondary lamellae ( 17 ) which surrounds the primary part ( 2 ), there being formed between the primary part ( 2 ) and the secondary part ( 8 ) a space ( 28 ) which contains a magnetorheological fluid, a regulatable magnetic field acting on the magnetorheological fluid. In order to have as small a build as possible, to be capable of transmitting a maximum torque with minimum current and to be easily controllable, at least one magnet coil ( 21 ) is arranged in front of or behind the lamellae ( 4, 17 ) in the axial direction and loops around a first U-shaped yoke ( 20 ), the two end faces ( 26 ) of which are on the same side of the lamellae and parallel to these, at least one second yoke ( 22 ) is on the side of the lamellae which faces away from the first yoke ( 20 ), and the regions of the secondary part ( 8 ) which lie inside and outside the lamellae ( 4, 17 ) in the radial direction consist of a material of low magnetic permeability.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No.10/532,379 filed Apr. 21, 2005, now U.S. Pat. No. 7,325,663, which is aNational Stage of International Application No. PCT/AT2003/000328 filedOct. 31, 2003, which claims the benefit of GM 739/2002 filed Oct. 31,2002. The disclosures of the above applications are incorporated hereinby reference.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

The invention relates to magnetorheological clutches which consist of astationary part, a rotatable primary part with primary lamellae, and asecondary part with secondary lamellae which is rotatable about a commonaxis and surrounds the primary part, there being formed between theprimary part and the secondary part a space which contains amagnetorheological fluid and in which primary lamellae and secondarylamellae alternate in the axial direction, and a magnet coil generatinga magnetic field of regulatable field strength which acts on themagnetorheological fluid.

However, for the use of a generic clutch in the drive train of a motorvehicle, current consumption and overall size are critical and musttherefore be minimized. In addition to this, there are also furtherrequirements: such as a wide regulating range of the transmitted torquethat, on the one hand, provide slip-free starting from standstill and,on the other hand, (also for reasons of noise), complete separation arepossible; and, finally, a rapid response in order to be compatible withelectronic drive dynamics controls (ESB, ABS, etc.).

Thus, U.S. Pat. No. 5,845,753 discloses a generic clutch, in which theyokes extend from one end face on one side of the clutch, so as tosurround this on the outside, as far as a second end face on the otherside of the clutch. This not only increases the diameter and weight, butalso means a large mass to be magnetized, thus consuming a large amountof current and resulting in the reduction of the magnetic field(disengagement) lasting too long for a usable control. Moreover, themagnetic force lines which pass through the space filled with themagnetorheological fluid are of low density and are distributed highlyunevenly.

The object of the invention is, therefore, to provide amagnetorheological clutch which avoids the disadvantages of the priorart and satisfies the above-specified requirements of the modern motorvehicle. The magnetorheological clutch should have as small a size aspossible, particularly in diameter, be capable of transmitting a maximumtorque with minimum current consumption, and yet be easily controllable.

SUMMARY

According to the invention, at least one magnet coil is arranged infront of or behind the lamellae in the axial direction, that is to sayapproximately on the same radius as these, said magnet coil loopingaround a first U-shaped yoke, the two end faces of which are on the sameside of the lamellae and parallel to these and are largely adjacent tothe lamellae, at least one second yoke is provided on the side of thelamellae which faces away from the first yoke, and the regions of thesecondary part which lie inside and outside the lamellae in the radialdirection consist of a material of low magnetic permeability.

The U-shaped yokes (there will, in practice, always be a plurality ofthese) cause a deflection of the magnetic field along the shortestpossible path and with a minimal iron volume to be magnetized. Thisresults in a minimal dead weight and low magnetic resistances. Moreover,the magnet coils which loop around only the U-shaped yokes can be ofvery small design, because a specific number of turns is required for aspecific magnetic field strength, which, in the case of the smalldiameter of the magnet coils, means short coil wire lengths and a lowerohmic resistance. Since the magnet coils lie outside the clutch, thereis a better discharge of heat.

The magnet coils lie in front of and behind the lamellae, and thereforethe outside diameter of the clutch is determined by the diameter of thelamellae. The second yokes arranged on the other side of the bundle oflamellae close the magnetic filed lines, so that the magnetic fieldlines, already short per se, pass twice through the bundle of lamellae,that is to say are “double-acting”. With the corresponding arrangementof the magnet coils, the field is highly dense and uniform over theentire area of the bundle of lamellae. The parts of the secondary partwhich consist of a material of low magnetic permeability prevent adispersion of the magnetic field.

Overall, therefore, the highest possible effective magnetic fieldstrength is obtained, along with the lowest possible current consumptionalso operable for the low-voltage on-board network of a motor vehicle,and along with a minimal overall size. A magnetic flux density of above0.7 [T] (=tesla) can be achieved. Moreover, the transmittable torque canbe increased by a rise in the number of lamellae, without anyappreciable enlargement of the clutch. In purely mechanical terms,however, the latter is large if only because of the large diameter ofthe lamellae lying outside the magnet coil.

For a further improvement in the profile of the field lines, anddepending on practical requirements (installation dimensions, torquerequirement), the cross section of the first U-shaped yokes may beincreased toward the end face, and the second yoke may be a flat bodyrunning in the circumferential direction and be surrounded by no magnetcoil. If the second yoke is also of U-shaped design and is surrounded bya magnet coil, a symmetrical field with a particularly high field linedensity is obtained.

In an advantageous embodiment of the invention, the at least one firstU-shaped yoke is connected to the secondary part and the end face of thefirst yoke forms the boundary wall of the space containing themagnetorheological fluid. The magnet coils thus rotate together with thesecondary part. This avoids the need for any air gap, which means aminimization of the magnetic losses. The second yoke then likewiserotates together with the secondary part, irrespective of whether it isdesigned to be U-shaped with a magnet coils or to be flat and without amagnet coil. In this case, an electrical brush connection is necessaryfor supplying the electrical current to the magnet coils.

In an alternative advantageous embodiment of the invention, the firstU-shaped yokes are connected to the stationary part and their end facesare adjacent to an annular region of the secondary part, thepermeability of which region is high, in contrast to the majority of thesecondary part. There is therefore no need for a brush connection, atthe expense of an air gap which, however, can be kept very small byvirtue of the arrangement according to the invention. The second yokesmay be designed likewise.

In a variant of the embodiment with the first yoke in the stationarypart, however, the second yokes may also be designed without a specificmagnet coil in the secondary part otherwise consisting of a material oflow permeability, since they then do not need any current supply and canrotate together with the secondary part. They are then either designedas flat bodies running in the circumferential direction or integrateddirectly into the secondary part.

The number of first and second yokes can be selected according torequirements. In practice, for reasons of symmetry, there will be atleast two; if there are more, then there will be even multiples of twofor polarity reasons. In an advantageous arrangement, their axes lietangentially in an axially normal plane. The legs of the yokes then lieon the same radius, thus making it easier to distribute the end facesover the annular area of the lamellae. The legs of the yokes could alsobe alternately on different radii if the densest possible packing on theannulus of the lamellae is to be achieved without a widening of thefeet.

In a development of the enlarged end face of the yokes, the end faces ofthe yokes are widened to form contact faces which almost adjoin oneanother and the inner and outer radius of which corresponds essentiallyto that of the lamellae. The entire annular area of these is thenutilized. The fact that the annular sectors only almost adjoin oneanother, that is to say do not touch one another, is for reasons ofpolarity. It is particularly beneficial if an even number of magnetcoils succeed one another in a polarity such that adjacent legs of theirU-shaped yokes form a common end face. This may be so both on one and onboth sides of the bundle of lamellae. They are then polarized in such away that field lines running through the two opposite yokes form aclosed curve.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 shows a longitudinal section through a first preferred embodimentof the subject of the invention,

FIG. 2 a shows a section according to line II-II, developed in order toillustrate the magnetic field lines,

FIG. 2 b is a graphical representation illustrating the magnetic fieldstrength corresponding to the magnetic field lines of FIG. 2 a,

FIG. 3 shows a variant of FIG. 1,

FIG. 4 shows a longitudinal section through a second embodiment of thesubject of the invention,

FIG. 5 shows a view of a first variant of the embodiments of FIGS. 1 and4, reduced,

FIG. 6 shows a section taken through line AA shown in FIG. 5,

FIG. 7 shows a view of a second variant of the embodiments of FIGS. 1and 4, reduced,

FIG. 8 shows a view of a third variant of the embodiments of FIGS. 1 and4, reduced, and

FIG. 9 shows a view of a fourth variant of the embodiments of FIGS. 1and 4, reduced.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses.

Of the stationary part 1, FIG. 1 depicts only the collar which makes thebrush contact for supplying the electrical current to the magnet coils.Torque transmission in the clutch takes place between a primary part 2and a secondary part 8. The primary part 2 is seated fixedly in terms ofrotation on a primary shaft 3 and forms a drum 5 with coupling teeth forthe rotationally fixed, but displaceable reception of the primarylamellae 4. The primary part 2 itself consists of a material of very lowmagnetic permeability, and the primary lamellae 4 consist of a materialof high magnetic permeability.

The secondary part 8 is screwed to the connecting flange 9 of asecondary shaft and receives the primary shaft 3 in bearings 10, 11. Thesecondary part 8 and primary part 2 are coaxial. The secondary part 8consists of a front cover 12, of a rear cover 13 and of acircumferential wall 14 which on one side is welded to the front cover12 and on the other side is connected to the rear cover 13 by means ofan annular nut 15. The circumferential wall 14 has on the inside acoupling toothing 16, in which the secondary lamellae 17 are arrangedfixedly in terms of rotation, but dispaceably.

The secondary part 8 has connected to it a first yoke 20 with a firstcoil 21 on the side of the front cover 12 and a second yoke 22 with asecond coil 23 on the side of the rear cover 13. The yokes 20, 22 (seeFIG. 2) are U-shaped, the coil 21, 23 loops around their middle part,and their legs 20′, 20″ extend parallel to the axis of rotation into thefront and rear covers 12, 13 respectively. The two yokes there form feet24, 25 which have a larger cross section than the legs of the yokes andwhich terminate in end faces 26, 27. The feet 24, 25 are connectedfixedly to the front and rear covers 12, 13 respectively and naturallyconsist of a material of high magnetic permeability, whereas the entiresecondary part 8, with the exception of the secondary lamellae 17,consists of a material of very low magnetic permeability.

A space 28 is thus formed, which contains alternately a number ofprimary lamellae 4 and secondary lamellae 17 and also contains amagnetorheological fluid. This space is delimited on the inside by thedrum 5 of this primary part, on the outside by the circumferential wall14 of the secondary part and at the front and rear by the inner walls ofthe front (12) and rear 13 cover and also the end faces 26, 27 of theyokes 20, 22. The part free of lamellae is filled with amagnetorheological fluid. Between the drum 5 of the primary part 2 andthe secondary part 8 are provided seals 29 which close off the space 28hermetically. Finally, for the protection of the magnet coils 21, 23, acorotating cladding plate 30 may also be provided.

FIGS. 2 a and 2 b illustrate a cylindrical section through the yokes 20,22 according to II-II (FIG. 2 a) and, above it, the magnetic fieldstrengths (FIG. 2 b). This section illustrates only the parts in whichthe magnetic field lines run and therefore those which consist of amaterial of high magnetic permeability. These are the yokes 20, 22 andthe alternating lamellae 4, 17. What can be seen are the U-shape of theyokes 20, 22 with legs 20′, 20″, and legs 22′, 22″, respectively, and athick closed curve 34 which indicates the direction and polarity of themagnetic field (counterclockwise). In the adjacent region on the left inthe figure, the field direction 35 is clockwise, that is to say oppositeto that of the yokes 20, 22. A plurality of field lines are alsoindicated here, so that a zone 36 in which the field strength has a zerocrossing can be seen.

This can be seen more clearly in the curve 38 lying above it in FIG. 2 bwhich illustrates the profile of the magnetic field strength along thecircumference. FIG. 2 is general in as much as four yokes distributed onthe circumference (as in FIG. 9) are provided. Only a single yoke or twoyokes or their multiple could also be provided, in order, within themeaning of the objective of the invention, to achieve, overall, as highand as uniformly distributed a magnetic field strength as possible inthe space 28 containing the lamellae.

FIG. 3 shows only the parts of high magnetic permeability, the rightyoke 22 of FIG. 1 being indicated only by broken lines. To be precise,it is also possible, within the scope of the invention, to be satisfiedwith a first yoke 20 with a coil 21, or a plurality of these, and todesign the second yoke 32 as a flat body or as a plate around which nomagnet coil is looped. This plate 32 then extends in a circumferentialdirection over the feet 24 of both legs 20′, 20″ of the yoke 20. Themagnetic flux is thereby also a closed curve again. In this case, anarrangement in which the plate 32 functions sometimes as a secondaryyoke and thereafter sometimes as a first yoke is also conceivable.

In the variant of FIG. 4, identical or similar parts are given thereference symbols of FIG. 1 increased by 100. In contrast to FIG. 1,here, the yokes 120, 122 are mounted in the stationary part 101, that isto say do not rotate. There is therefore no longer any need for brushcontacts. However, the feet 124, 125 of the yokes 120, 122 are separatedfrom the yokes themselves by air gaps 132, 133 which can nevertheless bekept very small by virtue of the arrangement according to the invention.The feet 124, 125 are introduced into the side walls 112, 113 of thesecondary part 108, so that the conditions in the space 128 are the sameagain as in FIG. 1. A further mounting 134 is provided between thestationary part 101 and the secondary part 108. With reference to thevariant of FIG. 3, the foot 125 alone may serve as a yoke if thecorresponding coil 123 is dispensed with.

FIG. 5 and FIG. 6 show the simplest design variant of the invention withonly two coils, of which the coil 21 can be seen on the front side ofthe secondary part 8 and the second, behind the secondary part 8, cannotbe seen, but is congruent with the first. The feet 24 of the yoke 20 arewidened here in the circumferential direction and extend such that theyform half of an annulus 50, 51. In this case, the symbols 52, 53indicate the polarity of the magnetic field. 52 is the flux directiontoward the observer and 53 the flux direction away from the observer.

It can also be seen in FIG. 6 that, in this case, the yoke 20 is not inone part, but consists of the two semiannular feet with their legs 20′and 20″ which receive, as a middle part of the U, a straight bolt 54,around which, in turn, the coil 21 is looped. Despite all itssimplicity, this embodiment has the disadvantage of generating a fieldof low homogeneity which exerts a tilting moment on the lamellae 4, 17.The directional arrows 52, 53 may be considered in this regard.

In the variant of FIG. 7, two magnet coils 21, 76 can be seen on thefront side of the secondary part. On the rear side of the latter, eitheralso two congruent coils or none are provided. See the variant of FIG.3. Here, again, the legs 20′ of the first coil 21 and 75′ of the secondcoil 76 are connected to a semicircular foot 70; and the other legs 20″,75″ of the two coils 21, 76 are connected to another semicircular foot71. However, the two halves of the annulus do not touch one another withtheir end faces, for, of course, they have different polarities 72, 73.On the rear side of the secondary part 8, the same feet, which cannot beseen, are likewise designed congruently with those which can be seen. Inthis variant, the field distribution is even more homogeneous, but atilting moment is still always exerted on the lamellae.

By increasing the number of coils, the individual coils may be ofsmaller design, which, in addition to the space saving, also entails asaving of weight, in particular of copper weight. What is critical forthe magnetic field strength, of course, is not the length of the wire,but the number of turns. In the case of a smaller diameter of the coiland the same number of turns, the length of the wire will naturally besmaller.

In the variant of FIG. 8, on the visible side, there are two coils 21,85, the yokes of which in each case again have two legs. Each of thelegs 20′, 20″, 84′, 84″ is widened into a specific foot 80, 81, 82, 83,each of which forms a quarter of an annulus. The individual feet shouldagain not touch one another. The arrows again indicate the polarity ofthe magnetic field. It can be seen that, in this arrangement, there isno longer a tilting moment exerted on the lamellae.

The variant of FIG. 9 has four small coils with their yokes 20, 94, 95,96, of which in each case one leg with the same polarity (for example20′, 94′) has a common foot 90 in the form of a quarter circle. Here,too, the annular sectors on the rear side of the secondary part 8 arecongruent and with or without a magnet coil. In the case of the fourmagnet coils shown (there could, however, even be a higher multiple oftwo), the magnet coils are very small, so that the inside diameter ofthe feet 90, 92, 93, 91 is scarcely exceeded, with the result that moreconstruction space is available for connecting the secondary shaft 9(FIG. 1) or other drive train parts.

Overall, in all the variants described, with a given current intensity,a maximum magnetic filed strength is afforded over the entire clutchspace, matching to practical requirements being possible by the choiceof one of the many variants described or their combinations. In allinstances, because of the arrangement of the magnet coils in front ofand behind the lamellae of the clutch (and not inside or outside thelatter), the construction space in the radial direction is alsorelatively small. This is particularly advantageous for use in the drivetrain of a motor vehicle.

1. A magnetorheological clutch comprising: a primary member and asecondary member forming a clutch cavity with at least one of saidprimary member and said secondary member being rotatably driven relativeto the other thereof; a magnetorheological fluid disposed in said clutchcavity; and a coil assembly operable to generate a magnetic field insaid clutch cavity, said magnetic field having a first polarity in afirst direction and a second polarity in a second direction differentfrom said first direction.
 2. The magnetorheological clutch of claim 1further including a primarily lamellae fixed to said primary member anda secondary lamellae fixed to said secondary member, said first andsecond lamellae disposed within said clutch cavity.
 3. Themagnetorheological clutch of claim 2 wherein said coil assembly is fixedto one of said primary and secondary members and includes a firstmagnetic coil located on one side of said clutch cavity and a secondmagnetic coil located on an opposite side of said clutch cavity.
 4. Themagnetorheological clutch of claim 3 wherein said first magnetic coil issupported by a first yoke having a first end face and a second end faceadjacent to said clutch cavity, wherein said first end face is polarizedin said first direction and said second end face is polarized in saidsecond direction.
 5. The magnetorheological clutch of claim 3 whereinsaid primary member is driven relative to said secondary member and saidcoil assembly is fixed to said secondary member.
 6. Themagnetorheological clutch of claim 5 wherein said secondary member isrotatable relative to said primary member.
 7. The magnetorheologicalclutch of claim 5 wherein said secondary member is non-rotatablerelative to said primary member.
 8. The magnetorheological clutch ofclaim 1 wherein said coil assembly is fixed to one of said primary andsecondary members and includes a first magnetic coil located on one sideof said clutch cavity and a second magnetic coil located on an oppositeside of said clutch cavity.
 9. The magnetorheological clutch of claim 8wherein said first magnetic coil is supported by a first yoke having afirst end face and a second end face adjacent to said clutch cavity,wherein said first end face is polarized in said first direction andsaid second end face is polarized in said second direction.
 10. Themagnetorheological clutch of claim 8 wherein said primary member isdriven relative to said secondary member and said coil assembly is fixedto said secondary member.
 11. The magnetorheological clutch of claim 10wherein said secondary member is rotatable relative to said primarymember.
 12. The magnetorheological clutch of claim 10 wherein saidsecondary member is non-rotatable relative to said primary member. 13.The magnetorheological clutch of claim 1 wherein said primary andsecondary are aligned about a common rotary axis, and wherein said coilassembly includes a magnetic coil having a center axis obliquelyoriented relative to said rotary axis.
 14. A magnetorheological clutchcomprising: a primary member and a secondary member aligned along acommon axis of rotation and forming a clutch cavity having axial endsand an outer diameter; and at least one coil assembly disposed adjacentto one of said axial ends and radially inboard of said outer diameter,said at least one coil assembly including a magnet coil having a centeraxis noncoincident to said axis of rotation.
 15. The magnetorheologicalclutch of claim 14 wherein said at least one coil assembly furtherincludes a yoke supporting said magnet coil, said yoke having aplurality of end faces disposed adjacent to said clutch cavity andradially inboard relative said outer diameter.
 16. Themagnetorheological clutch of claim 14 wherein said at least one coilassembly comprises a first coil assembly disposed adjacent to a firstaxial end of said clutch cavity and a second coil assembly disposedadjacent to a second axial end of said clutch cavity.
 17. Themagnetorheological clutch of claim 14 further including a primarilylamellae fixed to said primary member and a secondary lamellae fixed tosaid secondary member, said first and second lamellae disposed withinsaid clutch cavity.
 18. The magnetorheological clutch of claim 17wherein said coil assembly is fixed to one of said primary and secondarymembers and includes a first magnetic coil located on one side of saidclutch cavity and a second magnetic coil located on an opposite side ofsaid clutch cavity.
 19. The magnetorheological clutch of claim 18wherein said first magnetic coil is supported by a first yoke having afirst end face and a second end face adjacent to said clutch cavity,wherein said first end face is polarized in a first direction and saidsecond end face is polarized in a second direction.
 20. Themagnetorheological clutch of claim 14 wherein said primary member isdriven relative to said secondary member and said coil assembly is fixedto said secondary member.
 21. The magnetorheological clutch of claim 20wherein said secondary member is rotatable relative to said primarymember.
 22. The magnetorheological clutch of claim 20 wherein saidsecondary member is non-rotatable relative to said primary member.
 23. Amagnetorheological clutch comprising: a primary part with primarylamellae and a secondary part with secondary lamellae which surroundssaid primary part so as to define a space between said primary part andsaid secondary part which contains a magnetorheological fluid and inwhich said primary lamellae and secondary lamellae are disposed, and aregulatable magnetic field acting on said magnetorheological fluid,wherein a magnet coil is arranged in front or behind said lamellae inthe axial direction and loops around a first yoke having two end facesadjacent to and parallel to the lamellae, a second yoke is provided onthe side of said lamellae which faces away from said first yoke, andregions of said secondary part which lie inside and outside the lamellaein the radial direction consist of a material of low magneticpermeability.
 24. The magnetorheological clutch as claimed in claim 23wherein said second yoke is a flat body running in a circumferentialdirection and is surrounded by no magnet coil.
 25. Themagnetorheological clutch as claimed in claim 23 wherein said secondyoke is surrounded by a second magnet coil.
 26. The magnetorheologicalclutch as claimed in claim 23 wherein said first yoke is connected tosaid stationary part and is adjacent to an annular region of highpermeability of said secondary part.
 27. The magnetorheological clutchas claimed in claim 26 wherein said second yoke is also connected tosaid stationary part and is adjacent to an annular region of highpermeability of said secondary part.